1. Field of the Invention
The present invention relates to a polarization converter, an illumination optical device having the polarization converter and a projector.
2. Description of Related Art
Conventionally, a projector has often been used for presentation at a conference, academic society and exhibition. Such projector has a plurality of optical components in a casing, where a light beam irradiated by a light source is enlarged and projected after being modulated to form a projection image. A polarization converter for converting the light beam irradiated by the light source into uniform linearly polarization beam is used for enhancing utilization efficiency of the light beam to obtain a bright projection image.
The polarization converter has a polarizing conversion element having a polarization separating film inclined relative to incident light beam to transmit and reflect the light beam from a light source to separate into two linearly polarization beams, a reflecting film for reflecting the linearly polarization beam reflected by the polarization separating film, a light-transmissive member interposed between the polarization separating film and the reflecting film so that a plurality of the polarization separating films and the reflecting films are alternately arranged, a retardation plate adhered on light-irradiation side of the polarizing conversion element to convert a polarization axis of the light beam irradiated by the reflecting film, and a light-shielding mask provided on the light-incident side of the polarizing conversion element to shield the light beam from entering onto the reflecting film.
Such polarization converter is constructed as a unit having a polarizing conversion element body including the retardation plate and the polarizing conversion element, the light-shielding mask, and a holding frame for holding and housing the polarizing conversion element body and the light-shielding mask, the unit being housed in the optical parts housing.
According to the above arrangement, however, relative position between the polarizing conversion element body and the light-shielding mask has to be adjusted as well as the position between the holding frame and the optical parts housing, thus complicating the attachment process in the optical parts housing. Though it is possible to magnify the aperture ratio of the light-shielding mask for facilitating attachment process, the light-shielding function of the mask is deteriorated.